1. Field of the Invention
The present invention relates to an optical fingerprint authentication apparatus.
2. Related Art
Because one cost of today's widespread information system including making use of computers is the risk of leakage of confidential and private information and the danger of unauthorized access to confidential areas, there is an urgent need in our information-intensive society for identification and authorization of individuals.
Approaches to this problem are, for example, the input of a personal identification number (PIN) when using a cash card in an automatic teller machine of a bank, and the mandatory reading of an authorization card and input of a password when entering a computer room. However, with cards being used for a broad spectrum of functions, the management of cards held by individuals has become troublesome.
Additionally, individuals forget their PINs or passwords, and there is a danger that these will be leaked to or read by others.
The fingerprint has long been thought of as a good alternative to PINs and passwords as a means for individual authentication. The fingerprint can be thought of as high-level identification information, and identification information which, of course, the individual is not required to memorize or recall.
In a general fingerprint comparison apparatus, when a fingerprint is input using an image sensor, a recognition section performs image processing of the fingerprint, and detects characteristic points of the fingerprint, these being known as minutiae.
The similarity of the input fingerprint with a fingerprint in a database is calculated from the minutiae.
This similarity is represented by a value known as a score, the higher being the score, the greater being the similarity of the input fingerprint with a fingerprint in the database. If the score exceeds a prescribed threshold value, the input fingerprint is judged to be the same as the fingerprint stored in the database.
In a fingerprint identification apparatus as described above, however, it is not possible to distinguish between the fingerprint of an actual living person and a replica thereof (that is, a copy of a fingerprint created in a non-living medium).
For this reason, in a case in which it is possible to obtain a precise photograph of a fingerprint of a living person, for example, there is a danger that if this were to be input in place of an actual living fingerprint, the apparatus would erroneously recognize it as an actual living fingerprint.
In the past, various proposals have been made to avoid the above-noted problem. For example, in Japanese patent No. 2554667, directed at an “individual authentication apparatus” (hereinafter referred to as prior art example 1), the apparatus has means for measuring the temperature at the location of the living body at which the authentication is to be done (specifically, a thermocouple disposed in the fingerprint reading section), means for judging whether or not the measured temperature is within a pre-established body temperature range (30° C. to 38° C.), and means for performing a comparison for authentication only in the case in which the result of the judgment was that the measured temperature was within the pre-established range.
According to this technology, it is possible to achieve an individual authentication apparatus that does not recognize a fingerprint taken, for example from a photograph or a cut-off finger, that is, from a location other than a part of the actual body of the person to be authenticated.
Furthermore, this apparatus uses a contact-type method, in which a finger is brought into contact with a fingerprint reading section and the fingerprint is read.
In the Japanese unexamined patent publication (KOKAI) No.11-235452, directed at a “Lock opening apparatus with an identification function” (hereinafter referred to as the prior art example 2), there is language describing an optical fingerprint comparison apparatus for use as a security measure for an amusement location.
This optical fingerprint comparison apparatus shines illumination onto a fingerprint part of a finger brought into contact with a prism, the reflected light therefrom being guided to an image sensor, and the fingerprint pattern being detected therefrom.
This apparatus has means for making a fingerprint comparison between priorly stored fingerprint data and the fingerprint pattern pressed up against the prism, means for performing finger recognition, and a lock-opening means for opening a lock mechanism only when there is both coincidence resulting from the comparison by the fingerprint comparison means and finger identification by the finger identification means.
The finger identification means can be body temperature, pulse, fingernails and skin, and the shape of the finger.
Additionally, in the Japanese unexamined patent publication (KOKAI) No.10-187954, directed at a “All-in-one fingerprint reading system with a heating resistor” (hereinafter referred to as prior art example 3).
In contrast to the above-described contact-type system, in which the fingerprint reading means is separated from the means for measuring the temperature of the body part, the system of the Japanese unexamined patent publication (KOKAI) No.10-18795 combines these two elements. That is, a fingerprint reading sensor, up against which the finger is pressed, has an active surface of an element that is highly responsive to changes in temperature, and a built-in heating resistor for bringing about a transient temperature change in the sensitive element.
The thermal change caused by the heating resistor results in an electrical signal that differs, depending upon the thermal conductivity between the grooves and the raised portions of the lines of a fingerprint in contact with the sensing element matrix.
Fingerprint recognition is performed based on the above, and it is possible to recognize whether or not the fingerprint is from part of an actual living person during the fingerprint reading, via the characteristic heat released from a finger.
In the above-described prior art example 1, however, a thermocouple is used to detect the temperature of the object under measurement, and because a judgment is made that the object is an actual person if the temperature is within a prescribed temperature range (30° C. to 38° C.), if a fingerprint replica is raised to within the prescribed temperature, an erroneous judgment that the object is a human body will be made, thereby not solving the problem.
In the prior art example 2, a fingerprint pattern is recognized by an image sensor 106 using a non-contact method, and a detector 101 detects body temperature, pulse, or the like. In the case of body temperature detection, in the same manner as in the prior art example 1, it is possible to defeat this apparatus by simply warming up a replica.
In the case of pulse detection, the need to have quite a sensitive sensor to measure the pulse makes this device impractical. Additionally, even if such as device were achieved, the auxiliary detector (pulse detector) would become much more expensive than the image sensor, which is the main sensor, this also making the device impractical.
In the prior art example 3, the fingerprint reading section and the body temperature detector are combined as one. However, because of the use of an element sensitive to changes in temperature as the sensor that reads the fingerprint, this system is susceptible to changes in ambient temperature, making it necessary, for example, to change the threshold value between the summer and the winter, this presenting a problem in terms of maintenance.
Accordingly, it is an object of the present invention to solve the above-noted problems encountered the prior art, by providing stable fingerprint authentication, which is little influenced by the ambient temperature.
Another object of the present invention is to provide a fingerprint authentication apparatus that is maintenance free.